1. Field of the Invention
The present invention relates to a process for preparing 4-amino-1-naphthol ethers and novel intermediates.
2. Brief Description of the Prior Art
4-Amino-1-naphthol ethers are valuable intermediates in preparing active pharmaceutical ingredients (see, for example, WO 00/43384; B. Bachman, J. Wetzel, J. Org. Chem., 11,1946, p. 454-462; R. Herbst, P. Johnson, J. Org. Chem., 17, 1952, p. 693-697). The synthetic route disclosed, for example, by WO 00/43384 starts from 4-amino-1-naphthol hydrochloride and comprises the conversion of the amine to a protected derivative, the alkylation of the hydroxy group and then the cleavage of the protecting group. This process has the disadvantage that both the reactant and the protecting group reagents used are very expensive and the conversion to the desired 4-amino-1-naphthol ethers still requires three steps. The synthesis of 4-amino-1-methoxynaphtalene according to B. Bachman, J. Wetzel, J. Org. Chem., 11, 1946, p. 454-462 is similar and accordingly has the same disadvantages.
There is accordingly a need to develop an efficient process which, starting from inexpensive 1-naphthols, facilitates the preparation of 4-amino-1-naphthol ethers in a few steps.